A method used to determine the upper thermal boundary of subgrade based on boundary layer theory  

作　　者：QingBo Bai Xu Li YaHu Tian 

机构地区：[1]School of Civil Engineering,Beijing Jiaotong University [2]Qinghai Research and Observation Base,Key Laboratory of Highway Construction & Maintenance Technology in Permafrost Regions,Ministry of Transport

出　　处：《Research in Cold and Arid Regions》2015年第4期384-391,共8页寒旱区科学（英文版）

基　　金：supported by the National Natural Science Foundation of China (Nos. 51378057, 41371081, and 41171064);the National Key Basic Research Program of China (973 Program, No. 2012CB026104)

摘　　要：In the numerical simulation of long-term subgrade temperature fields, the daily variation of soil temperature at a certain depth h is negligible. Such phenomenon is called the ＂boundary layer theory.＂ Depth h is defined as the boundary layer thickness and the soil temperature at h is approximately equal to a temperature increment plus the average atmosphere temperature. In the past, the boundary layer thickness and temperature increment were usually extracted from monitored data in the field. In this paper, a method is proposed to determinate the boundary layer thickness and temperature incre- ment. Based on the typical designs of highway or railway, the theoretical solution of boundary layer thickness is inferred and listed. Further, the empirical equation and design chart for determining the temperature increment are given in which the following factors are addressed, including solar radiation, equivalent thermal diffusivity and convective heat-transfer coefficient. Using these equations or design charts, the boundary layer thickness and temperature increment can be easily determined and used in the simulation of long-term subgrade temperature fields. Finally, an example is conducted and used to verify the method. The result shows that the proposed method for determining the upper thermal boundary of subgrade is accurate and practical.In the numerical simulation of long-term subgrade temperature fields, the daily variation of soil temperature at a certain depth h is negligible. Such phenomenon is called the ＂boundary layer theory.＂ Depth h is defined as the boundary layer thickness and the soil temperature at h is approximately equal to a temperature increment plus the average atmosphere temperature. In the past, the boundary layer thickness and temperature increment were usually extracted from monitored data in the field. In this paper, a method is proposed to determinate the boundary layer thickness and temperature incre- ment. Based on the typical designs of highway or railway, the theoretical solution of boundary layer thickness is inferred and listed. Further, the empirical equation and design chart for determining the temperature increment are given in which the following factors are addressed, including solar radiation, equivalent thermal diffusivity and convective heat-transfer coefficient. Using these equations or design charts, the boundary layer thickness and temperature increment can be easily determined and used in the simulation of long-term subgrade temperature fields. Finally, an example is conducted and used to verify the method. The result shows that the proposed method for determining the upper thermal boundary of subgrade is accurate and practical.

关 键 词：temperature field boundary layer PERMAFROST SUBGRADE equivalent thermal diffusivity 

分 类 号：U213.14[交通运输工程—道路与铁道工程] U416.16